Preparation process of alumina

First, seed crystal aluminium hydroxide is produced through simultaneous and continuous adding of aluminium compound and acid or alkali solution, controlling pH value in certain value in the range 6-11 and producing colloid in cocurrent flow. Then, noncrystalline aluminium hydroxide and fine particle are dissolved by adding acid or alkali solution to regulate pH value to greater than 11 or lower than 4; and finally, both dissolved and newly added aluminium ions re-precipitate under the action of seed crystal by re-adding acid or alkali solution to regulate pH value to 6-11. Repeating the above said steps for 1-20 times and through ageing, washing, filtration, drying, forming and roast, alumina product is produced.